Brazing is a group of welding processes wherein the filler metal is generally a non-ferrous metal or alloy whose melting point is higher than 840.degree. F., but lower than that of the metal or alloys to be joined. At one extreme, brazing is similar to soldering and is sometimes called hard soldering. Joints to be soldered are usually designed to require a thin film of filler metal which is drawn into the joint by capillary action when the solder becomes molten. This principal is also used in brazing in that a high-temperature process uses a brazing material to join close-fitting parts, such as steel parts. Most forms of brazing depend on local heating with a torch or by other means while some brazing is generally done in a furnace in which the parts are heated to a high temperature such as 1600.degree. F.
Another type of brazing is similar to welding in many respects and is sometimes called bronze welding. The joints are generally V-shaped in which a bead of filler metal is deposited. This technique differs from welding in that the base metal is not melted but only raised to the "tinning" temperature at which bonding takes place between the base metal and the filler metal by slight interdiffusion or alloying.
Braze filler metal pastes are generally custom blends of filler metal with a chemical neutral gel. A majority of the gels used in braze filler metal pastes employ organic solvent-based binders in which the solvent could be toluene, methyl ethyl ketone, acetone, alcohols, trichloroethane, and the like. Many of these organic solvents are hazardous to both personal health and the environment.
Brazing cements for use with powdered brazing filler metals are commercially available in many different viscosities. The brazing cement could be a liquid plastic that provides a means of applying powdered brazing filler metals in an easy-to-use liquid powder mixture. The brazing cement acts as both a vehicle and a binder so that when mixed with a powdered brazing filler metal, the mixture can be applied by a brush, eyedropper, syringe, spray gun or the like to specific areas to be bonded. The viscosity of the cement for use will depend on the amount of filler metal required in a joint area. The more viscous the cement, the more filler metal can be carried. As stated above, the majority of these cements using organic solvents that are hazardous to both personal health and the environment.
It is an object of the present invention to provide a braze filler metal paste comprising braze metal powder dispersed in an aqueous gel composed of a binder and a dispersant that is not hazardous to the environment or personal health.
Another object of the present invention is to provide a braze filler metal paste that has a suitable viscosity so that the paste can be packaged within a conventional tube container so that it can be dispersed when needed.
Another object of the present invention is to provide a braze filler metal paste that is cost effective to produce and easy to apply.
The above and further objects will become apparent upon consideration of the following description.